You're going to have software for a modern, efficient car, whether you like it or not. For the engine (fuel injection alone needs a bunch of software), ABS, traction control, A/C, and countless other things. And whether your radio has physical buttons or not, unless that physical button is on a radio from the 1980s and directly controls a variable capacitor and a belt to a frequency indicator, it's going to have software.
Of course we had cars entirely without software, about 50 years ago. But they were slow, had many quirks, and absolutely massive relative fuel consumption compared to today.
I think this nomenclature is a result of the post-Jobs software as "app" paradigm + Web as the definitive "application" platform era.
The majority of software written, especially in these circles, is going to be some sort of user interface/CRUD stuff. The "invisible" (and frankly remarkable, when talking of things like ECUs and ABS software) is basically like The Earth (it's just always been there and taken for granted).
Your engine control, your ABS and your traction control all run software (or "firmware", whatever that word means in this age) and they have been for decades.
What needs to stop is that awful trend tesla started where they replace the entire dashboard with a tablet.
And anyways, merely auditing I serious doubt would be effective. (LGTM, ship it!)
2. The German car industry already successfully teamed up on sharing map data (https://www.here.com/).
3. However, while this may work for Libre Office installs in a city administration and (non-critical) car infotainment software, this likely cannot work for the most important automotive control software, due to the legal responsibility of the car manufacturer (they would need to review/audit all changes of open source contributors line by line, patch by patch) - because bugs can cost lives there.